A room temperature Bose-Einstein condensate2/22/2013
ANN ARBOR – Michigan Engineering researchers have created what they believe to be the first near-equilibrium room temperature Bose-Einstein condensate – a unique and special state of matter in which a group of particles behaves as one massive particle, giving scientists the rare opportunity to directly observe quantum phenomena.
A paper on the research is published in Proceedings of the National Academy of Sciences.
Typically, Bose-Einstein condensates must be created at supercold temperatures, so the ability to produce them at room temperature makes them easier and cheaper to make.
Aside from giving researchers a window into the quantum realm, Bose-Einstein condensates and the light they emit could potentially be controlled and used for sensitive instrumentation and measurements in the future.
“Our experiment was done with a very thin wire – a nanowire – made of aluminum, gallium and nitrogen. Thus it is an alloy (AlGaN) nanowire, but with varying amounts of aluminum and gallium along its length to form a trap in a small section of the nanowire where there was no aluminum,” explained Pallab Bhattacharya, the Charles M. Vest Distinguished University Professor of Electrical Engineering and Computer Science and an author of the paper.
The researchers buried the nanowire in a bowl-shaped, reflective device called a dielectric resonant cavity. Then they shined light on the nanowire to excite particles on its high aluminum content end. The light reflecting in the cavity coupled with exciton particles in the nanowire. An exciton is an electron bound to a “hole,” or place where an electron used to be. Together the photons and excitons produced polaritons. A polariton is not exactly a particle, but it behaves as if it were. It is a “coupled quantum mechanical state” between an excited molecule and a photon, or particle of light. These polaritons then diffuse and drift towards the trap in the nanowire.
“As the polaritons move along the nanowire, the ones with the highest energy exit the cavity as light, enabling evaporative cooling and ensuring that the coldest polaritons reach the bottom of the trap to form a near-equilibrium Bose-Einstein condensate at room temperature,” Bhattacharya continued. “Thus evaporative cooling is accomplished here by gradually varying the electronic properties of the material in the nanowire along its length.”
The paper is titled “Polariton Bose–Einstein condensate at room temperature in an Al(Ga)N nanowire–dielectric microcavity with a spatial potential trap.” The full text is available at http://www.pnas.org/content/110/8/2735. The work is funded by the National Science Foundation Materials Research Science and Engineering Center at the University of Michigan.
About Michigan Engineering: The University of Michigan College of Engineering is one of the top engineering schools in the country. Eight academic departments are ranked in the nation's top 10 -- some twice for different programs. Its research budget is one of the largest of any public university. Its faculty and students are making a difference at the frontiers of fields as diverse as nanotechnology, sustainability, healthcare, national security and robotics. They are involved in spacecraft missions across the solar system, and have developed partnerships with automotive industry leaders to transform transportation. Its entrepreneurial culture encourages faculty and students alike to move their innovations beyond the laboratory and into the real world to benefit society. Its alumni base of nearly 70,000 spans the globe.